1. Field of the Invention
The invention pertains to the field of pumps for dispensing liquids. More particularly, the invention pertains to positive-displacement pumps.
2. Description of Related Art
In all beverage dispensers using liquid concentrate, from which beverages are extracted by hot or cold water, the dispensing of the concentrate liquid is done by a “pump”. The most common is a peristaltic pump. The pump is part of the dispenser and the concentrate liquid bag is connected to the pump on one side and the mixing water on the other side via special plastic tubing.
In order to ensure a high quality beverage dispenser it is essential to clean and sanitize especially the concentrate liquid dispensing system periodically to avoid the growth of bacteria which might be harmful to the customers and degrade the quality of the dispensed beverage. In the current liquid concentrate beverage dispensers, the cleaning procedure is labor intensive and requires basic technical skills that in most cases the service personnel do not have. Therefore the cleaning and sanitize procedure is done very rarely.
A second important requirement of a beverage dispenser which uses concentrate liquid is to achieve consistency in the mixing ratio for each cup. This requires concentrate liquid dispensing pump that will be able to change the dispensing rate of the concentrate liquid instantly and with very fine resolution on order of 1% or better. Such a pump is relatively expensive and requires sophisticate controller. Also it is desired to have a pump with large dynamical range.
It is known to include a pump or valve as part of a removable fluid reservoir in a dispensing system. These pumps are often incorporated into the reservoir structure, or built into a spout, dispensing tube or cap for the reservoir. In some cases, the pumps are designed to be disposable or recyclable with the reservoir. Some examples are shown in the following US patents:
U.S. Pat. No. 2,254,833 “Method and Apparatus for Controlling Intermittent Fluid Flow” (1941) shows a solenoid-actuated valve in a hospital intranasal feeding system. A solenoid coil surrounds the tube leading from the drip bottle, and valve is formed by a metallic member in the tube. The metallic member is reciprocated by electrical pulses in the coil, releasing quantities of liquid when the solenoid is actuated.
U.S. Pat. No. 2,887,255 “Liquid Measuring Device” (1959) is a washing-machine detergent dispenser. A solenoid coil surrounds an armature in a chamber, all formed into cap of detergent bottle. Detergent fills the chamber when the solenoid is inactive, allowing the armature to block the outflow from the chamber. When the coil is actuated, the armature moves up, blocking detergent flow into the chamber, and allowing the chamber to drain, dispensing a measured portion of detergent.
U.S. Pat. No. 3,258,166 “Dispenser for Liquids” (1966) shows a valve within an elongated spout of a jar for a liquid dispenser. A coil surrounds the spout and reciprocates the valve: “ . . . while it oscillates the armature acts not unlike the plunger of a pump and actually forces the liquid through the nipple . . . is of particular advantage when the liquid is coffee extract . . . ” If this design were used in a bag-in-box application, air can enter from the bottom of the spout when the valve is up—vents are provided in the rigid jar used in this patent which are not available in the bag-in-box. Also, this design relies on the liquid height in the vented jar to return the valve to its seat, so that the amount of liquid dispensed would vary depending on the amount of liquid in the reservoir, which would make it difficult to dispense consistent amounts of liquid.
U.S. Pat. No. 4,393,982 “Metered Dispensing of Liquids” (1983) uses a coil surrounding a dispensing tube. A disk-like armature is attracted by the coil to compress a bellows in the tube to pump liquid. This design requires one-way valves above and below the bellows, which can become clogged, especially with more viscous liquids like concentrated beverages or soap.
U.S. Pat. No. 4,450,987 “Portion Control Liquid Dispenser” (1984) uses a solenoid coil surrounding a valve armature in a tube from a bag-in-box. The armature is purely a valve, and liquid runs out of the bag by gravity when the valve is open, it is not pumped. This is similar to U.S. Pat. No. 4,921,131 “Liquid Dispenser” (1990), which is a soap dispenser which also uses a solenoid coil to operate an armature acting as a valve in the bag tube.
U.S. Pat. No. 5,114,047 “Pump and Mixing Device for Liquids” (1992) is part of a juice dispensing system in which a plastic reservoir for juice concentrate is sold with an integrated disposable pump. A single compressible chamber acts as a pump, compressed by a lever arm leading from a motor. The pump design of this patent requires one-way valves, with the disadvantages explained previously. A continuation-in-part, U.S. Pat. No. 5,275,309 “One Way Valve with Unitary Valve Element” (1994) shows details of a number of embodiments of these valves.
U.S. Pat. No. 5,615,801 “Juice Concentrate Package for Postmix Dispenser” (1997) is another example of a disposable pump which is part of a bag-in-box system. The pump is a “Progressive Cavity” pump.